1. Field of the Invention
The present invention relates to mechanisms for selectively altering the axial positioning of a translatable member between an axially biased first position and a second position in opposition to said axial bias, and for releasably locking said translatable member in at least said second position. More particularly, the present invention provides an improved type of such a mechanism which may be readily manually operated so as to be especially adaptable for use with conventional power wheel hub assemblies of vehicles and implements.
2. Description of the Prior Art
In vehicles of several types and in certain agricultural implements, it is often advantageous to provide certain powered axles with mechanisms enabling a hub associated with such powered axle to selectively assume either a powered or a free-wheeling operating condition. Heretofore, several well-known mechanisms have been described in the prior art, each intended to cooperate with a power wheel hub assembly to selectively engage or disengage the hub from the axle. In such power wheel assemblies, a rotational motion of the axle is generally communicated to the hub by the engagement of a clutch plate carried by the axle with a matching plate carried by the which engages with a matching set of internal splines formed in the hub. In either case, when it is desired to provide for unpowered or "free-wheeling" rotation of the hub about the axle, the axle is typically formed as an axially shiftable power shaft, axially biased to maintain engagement of the friction clutch or splines.
Conventional hub disengagement assemblies associated with such mechanisms typically include a plunger, acting in a direction along the axis of the power shaft, which plunger is adapted to be axially shifted along with the power shaft, either outwardly under the influence of the bias upon the power shaft or inwardly in opposition to such bias. Means are typically provided to maintain the plunger in a substantially outwardly translated position, corresponding to a status of engagement of the power shaft with the hub, or an inwardly translated position, corresponding to an axial translation of the power shaft at which the power shaft is disengaged from the hub.
Several examples of known prior art have been heretofore available to perform the function of translating the axially shiftable power shaft between its engaged and disengaged positions. The simplest form employs a reversibly mounted plate having a projection on one side thereof. When the plate is mounted such that the projection extends outwardly from the hub, the axial bias applied to the axially shifted power shaft urges an extension affixed to or formed on the end of the axially shiftable power shaft to translate outwardly into a recess formed by the projection on the plate such that the power shaft is engaged with the hub for the communication of rotation thereto. When the plate is mounted onto the hub such that the projection is disposed inwardly with respect to the hub, the projection pushes the extension on the end cf the axially shiftable power shaft in opposition to the bias and into an axially translated position whereat the power shaft is disengaged from the hub. It can be noted that the use of such an approach to switch from an engaged condition to a disengaged condition requires that the plate be removed, reversed, and remounted at each desired change from an engaged to a disengaged status, or the reverse.
The known prior art most nearly analogous to the present invention is represented by the hub disengaging apparatus described in U.S. Pat. No. 4,453,852. In the described apparatus, a housing is mounted to a hub so as to support a centrally disposed translatable plunger in a cavity of said housing such that said plunger is aligned to translate in concert with the distal end of an axially shiftable power shaft. The plunger is configured to have at least two diameters, the lesser diameter extending outwardly from the housing, whereas the greater diameter is restrained from further outward translation by the housing. The plunger is urged to this position by the typical axial bias acting on the power shaft, thereby allowing the power shaft to assume an engaged position with respect to the hub. At least one additional translatable plunger is disposed within an annular region of the housing such that said additional plungers are translatable along axes parallel to and equidistantly spaced apart from the axis of translation of the centrally disposed plunger. Each of said additional plungers, generally not exceeding two in number, are disposed within a respective generally cylindrical bore formed through the housing. Passages are formed radially between each bore containing an additional plunger and the cavity in which the central plunger translates. Said passages retain interlocking elements which, in the aforesaid engaged condition of the power shaft with the hub, rest against the greater diameter of the central plunger. Additionally, in said condition, said interlocking elements rest within grooves of reduced diameter formed appropriately in each of the additional plungers at an axial position of substantially maximum inward translation of each of the additional plungers. Each of the additional plungers is provided with a bias acting between the hub and each plunger urging each additional plunger in an outward direction. However, in the engaged condition, outward translation of the additional plungers is precluded by the interlocking elements resting against the greater diameter of the central plunger and constrained within their respective communicating passages so as to be held within the grooves of the additional plungers, thereby holding the additional plungers at their inwardly translated positions.
When it is desired to disengage the power shaft from the hub, the central plunger is inwardly depressed, in opposition to the axial bias exerted on the power shaft, through a distance sufficient to disengage the clutch or splines of the power shaft from the hub. During that portion of the inward translation of the central plunger in which the power shaft and hub retain some measure of engagement, the interlocking elements are held in their engaged positions by a longitudinal extent of the central plunger having the aforesaid greater diameter. When the power shaft reaches its disengaged position with respect to the hub, the lesser diameter axial extent of the central plunger is disposed axially adjacent the communicating passages holding the interlocking elements. Under urging of the biases acting on each of the additional plungers, the interlocking elements tend to be forced out of the grooves in the additional plungers by beveled shoulders of the grooves so as to translate through the communicating passages to rest against the lesser diameter of the central plunger. When the interlocking elements have so transversely translated as to be clear of the grooves in the additional plungers, the additional plungers are urged outwardly by their respective biases so as to bring a full diameter surface of each of the additional plungers into contact with its respective interlocking element, thereby holding the interlocking elements against the lesser diameter of the central plunger, precluding the central plunger from moving outwardly under urging of the axial bias applied to the power shaft. Thus the central plunger is locked in a disengaged position.
To return the disengaging apparatus to an engaged position, the additional plungers are simultaneously pushed inwardly, in opposition to their respective biases, until their respective grooves have been longitudinally translated to be aligned with the interlocking elements. Thereat the axial bias means acting on the power shaft urges the power shaft and the central plunger to translate in an outward direction which in turn causes the interlocking elements to ride along a beveled shoulder between the lesser and greater diameters of the central plunger so as to be transversely translated into the respective grooves of the additional plungers. When the interlocking elements are so fully translated, the central plunger may continue its outward axial translation, enabling the power shaft to become engaged with the hub, the additional plungers being retained in their inward positions by the interlocking elements as has been described above.
It can be readily observed from a more detailed study of U.S. Pat. No. 4,453,852 that such a design provides for rapid selection of either an engaged position or a disengaged position of the power shaft with respect to the hub, without resort to disassembly or reassembly of the disengaging apparatus. However, the complexity of such apparatus may tend to require significant fabrication costs. Moreover, significant effort is required during fabrication to ensure that the interlocking elements are capable of substantially free transverse translation which implies that the surfaces of the beveled shoulders of the grooves in the additional plungers and the shoulder between the lesser and greater diameters of the central plunger, together with the surfaces of the communicating passages through which the interlocking elements are transversely translatable, be of a low friction finish. Additionally, care must be taken during fabrication, use, and assembly so as to preclude the introduction of foreign materials which may impede the transverse translation of the interlocking elements or the axial translations of the several plungers.